The valve opening point, at which an electronic expansion valve is switched from the closed state to the open state, varies from one electronic expansion valve to another. Such variation is caused by variations in the manner in which a stepper motor is installed and variations in the dimensions of valve members and valve seats.
Such varied valve opening points of electronic expansion valves cause variation in performance of air conditioners. Even in the same type of air conditioners having refrigerant circuits controlled according to a common control program, valve opening points of electronic expansion valves installed in the air conditioners generally vary from one product to another. As a result, even when the same pulse control is performed on the electronic expansion valves, the respective electronic expansion valves bring about varied refrigerant flow rates. This causes an inappropriate refrigerant flow rate in some air conditioners, thus destabilizing air conditioning.
To decrease the number of unstably operating air conditioners, air conditioning by respective air conditioners must be controlled based on the valve opening point of the electronic expansion valve, which is installed in each of the air conditioners.
Accordingly, as described in Patent Document 1, to accurately obtain the valve opening point of an electronic expansion valve installed in an air conditioner, the valve opening point of the electronic expansion valve is measured. Specifically, the temperature of the heat exchanger installed in an indoor unit of the air conditioner is detected and, meanwhile, the pulse number input to the stepper motor of the electronic expansion valve is increased in a stepwise manner. Then, the valve opening point is set based on the pulse number at the time when the temperature of the heat exchanger of the indoor unit decreases by an amount greater than or equal to a predetermined amount.
To accurately measure the valve opening point, the temperature in the environment surrounding the refrigerant circuit must be maintained constant throughout a measuring period. In other words, the ambient temperature of the indoor heat exchanger and the ambient temperature of an outdoor heat exchanger must be maintained unchanged for a predetermined period of time. However, when the air conditioner is in operation, the ambient temperatures of the indoor and outdoor heat exchangers are substantially impossible to maintain constant. This hampers accurate measurement of the valve opening point and thus makes it difficult for the air conditioner to perform appropriate air conditioning control in accordance with the valve opening point of the electronic expansion valve. As a result, an electronic expansion valve capable of allowing such appropriate air conditioning control is demanded.